U.S. Pat. No. 6,734,532 entitled “Back Side Coating Of Semiconductor Wafers” (“the '532 patent”) discusses a semiconductor device including a semiconductor chip having an active and a passive surface (or side). The active surface includes an integrated circuit (I/C) and input/output (I/O) pads suitable for metallurgical contacts. Further, the device has a protective plastic film of controlled and uniform thickness selectively attached to the passive surface. The film is suitable to absorb light of visible and ultraviolet wavelengths, to remain insensitive to moisture absorption, and to exert thermomechanical stress on the chip such that this stress at least partially neutralizes the stress exerted by an outside part after chip assembly. The plastic film of the '532 patent is selected from a group of electrically insulating materials including polyimide, epoxy resin, and silicone, and the film may further include hardener, tackyfier, and fillers.
The plastic film thickness of the '532 patent preferably ranges from 20 to 60 μm (micrometers), the light absorption is at least 96%, and the neutralizing stress is provided by a film Coefficient of Thermal Expansion (CTE) of about 18 to 45 ppm/degree C., approximately matching the CTE of the outside part, such as a printed wiring board. After curing, the film has an adhesion strength of about 400 kg/cm2 and a modulus of about 16 GPa.
The plastic film is rolled onto the passive surface of the whole semiconductor wafer and cured at elevated temperatures, preferably about 150 degree C., for a length of time of about 1 hour. After film hardening, the wafer sawing process is applied to the semiconductor and film material concurrently in order to singulate the individual chips. The disclosure of the '532 patent is hereby incorporated herein in its entirety by reference.
U.S. Pat. No. 6,023,094 entitled “Semiconductor Wafer Having A Bottom Surface Protective Layer” (the '094 patent) discusses a packaged integrated circuit device. The disclosure of the '094 patent is hereby incorporated herein in its entirety by reference.